1. Field of the Invention
The present invention relates to a semiconductor optical device obtained by forming a p-n junction on a semiconductor substrate.
2. Description of Related Art
LED (Light Emitting Diode) is an example known as a semiconductor optical device.
In the case of the LED 3300 in FIG. 33, a multi-layered substrate, comprised of a GaAs1xe2x88x92xPx inclined layer 3312 and a GaAs1xe2x88x92yPy layer 3313, which are grown by epitaxy on a GaAs substrate 3311, is used as an n-type semiconductor substrate 3310. The GaAs1xe2x88x92xPx inclined layer 3312 is formed such that the phosphorus composition ratio increases as it approaches the top face of the layer. Near the surface of the GaAs1xe2x88x92xPy layer 3313, a p-type area 3320 is formed by, for example, selectively diffusing such a p-type impurity as zinc. The surface of the GaAs1xe2x88x92yPy layer 3313 is covered with a interlayer insulator 3330, except for a part of the p-type area 3320. On the area where the diffusion area 3320 is exposed, a p-type electrode 3340 is formed. On the rear face of the GaAs substrate 3311, an electrode 3350 is formed.
As shown in FIG. 33, when the p-type area 3320 is formed by a diffusion method, a p-n junction interface 3321 in the longitudinal direction and a p-n junction interface 3322 in the lateral direction are formed in the semiconductor substrate 3310. The p-n junction interface 3321 in the longitudinal direction mainly contributes to emission at a deep position in the GaAs1xe2x88x92yPy layer 3313. The p-n junction interface 3322 in the lateral direction mainly contributes to emission at a shallow position, that is, near the surface of the GaAs1xe2x88x92yPy layer 3313.
A shallow position of the layer 3313 has a high density of crystal defects which are generated by the diffusion of the p-type impurity, therefore the recombination rate of carriers is low, which makes the emission efficiency poor. To increase the emission efficiency of the LED 3300, causing emission at a deep position of the GaAs1xe2x88x92yPy layer 3313 is preferable.
However, in the p-n junction interface 3322, at a very shallow position of the GaAs1xe2x88x92yPy layer, a microscopic turbulence of forms exists. This turbulence makes the electric field very high and tends to cause a concentration of carriers. Therefore, in the LED 3300, carriers tend to concentrate at a very shallow position in the layer 3313, making the emission efficiency poor.
An object of the present invention is to increase the emission efficiency of a semiconductor optical device.
To achieve this object, a semiconductor optical device in accordance with the present invention comprises: a semiconductor substrate having a first conductive type semiconductor layer; a second conductive area formed in the semiconductor layer by doping a second conductive type impurity, which is a different conductive type from the first conductive type, selectively from the surface of the semiconductor substrate; and an etched area formed at the interface between the second conductive type area and the other area near the surface of the semiconductor substrate.
By forming the etched area, the area near the surface of the semiconductor substrate is removed from the interface between the second conductive type area and the other area. This can improve the emission efficiency of the semiconductor device.